It is known that long metal products, that is having a predominant longitudinal size with respect to the cross section, are normally produced by rolling long semifinished products deriving from continuous casting of the metal, for example steel.
The finished products are generally bars, round pieces for reinforced concrete, rods, beams or other profiles, obtained by transforming billets or blumes, with a square, rectangular or round section.
Steel plants are known for the production of long products in which a rolling mill is connected to a continuous casting machine downstream of the latter in a work direction.
In these known plants, a rolling line is located downstream of a continuous casting line, and can be for example aligned and directly coupled with it, defining a co-rolling line, thus without providing intermediate devices, transfer devices, shuttles, translating planes, mobile rollerways or other, which actively move the cast metal, for example translating it in directions transverse to the work direction.
These known plants can perform a production process with no solution of continuity, also known as “endless”, in which there is only one semifinished continuous cast product which extends from the zone where the liquid steel solidifies to a zone where it enters into the rolling mill.
The single semifinished product is rolled progressively along the rolling line downstream of the continuous casting line, allowing to reduce the number of entrances over all the stands of the rolling train and hence the probability of cobbles occurring, thus allowing high productivity.
The known combined plant also allows to reduce the compression powers needed in the first portion of the rolling mill, and to exploit the high temperature of the semifinished cast product and to reduce the quantity of cropping cuts, allowing to contain operating costs thanks to increased yield.
Furthermore, a plant provided with a co-rolling line can also perform a semi-endless production process, in which, instead of a single continuous semifinished product, the rolling mill receives, from the continuous casting, material defined by a discrete succession of semifinished products, sheared to size by a shearing unit.
The shearing unit can be used in the starting and stopping phases of the casting machine, for example to perform the head and tail cropping, or when there is a stoppage of the rolling mill, for example following a maintenance intervention or equipping of the plant, or following a cobble or other problem or inconvenience.
In such situations, where the rolling mill is not able to receive material to be rolled, semifinished cast products are produced, using the shearing unit as above, which have a certain pre-established length and which are then sent to storage areas to be subsequently worked in the rolling mill, once it has been returned to service.
Plants are also known in which two casting lines feed a rolling line downstream of the casting machine and work with a semi-endless process.
With the aim of producing competitive products, there is a strongly felt need to increase the productivity of steel plants, and also to contain waste and energy consumption in order to increase the yield and reduce production costs.
Known combined continuous casting and rolling plants can be limited in this sense, since they are unable to satisfy this requirement, and are greatly affected by stoppages, either programmed or accidental, of the rolling mill.
This limitation as above is particularly important especially in the case of steel plants with a single co-rolling line, in which any delay or problem in rolling can cause the slow-down or stoppage of the continuous casting machine upstream and, consequently, also of the whole steel works served by each steel plant.
Furthermore, if an increase in hourly productivity is required from the mono-line steel plant, this increase can be obtained only by increasing the casting speed. Increasing the casting speed has a technological limit, however, determined for each continuous casting machine and for each type of product, by the fact that too high speeds penalize the castability of the semifinished cast product, even making it impossible, and also compromise the quality thereof, with consequent negative effects on the rolling process and hence on the quality of the finished product.
U.S. 2004/079512 A1, JP S56 45201 A and JP S55 112105 A describe multiple line continuous casting plants. US 2004/079512 A1 proposes a solution in which two rolling lines disposed angled with respect to each other, for example by 90°, are fed by a respective casting device with twin rolls fed by a tundish connected to a double ladle rotatable device. JP S56 45201 A and JP S55 112105 A describe solutions with a double casting and roughing line, which converge in a single intermediate rolling and finishing train, a system being provided to control the loop between the roughing rolling stands and the intermediate and finishing rolling stands.
One purpose of the present invention is to obtain a combined continuous casting and rolling plant, and the corresponding method, for the production of long metal products that guarantee high productivity and reduce to a minimum the spaces occupied.
Another purpose of the present invention is to exploit to the utmost the cycle of the steel plant upstream, minimizing the number of movements necessary to feed the casting machines located downstream.
Another purpose of the present invention is to maximize the yield of the plant and the corresponding method, reducing to a minimum the discards of material during the working process.
Another purpose of the present invention is to exploit to the maximum the enthalpy possessed by the original liquid steel, in particular of the semifinished continuous casting products, to contain the running costs and the energy consumption of the plant.
Furthermore, another purpose of the present invention is to obtain a steel plant and a corresponding method of production for the production of long metal products that is flexible, so that it is possible to perform for example a plurality of production steps adaptably to a plurality of different functioning conditions or type of product to be made.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.